A printed circuit board (PCB) typically consists of one or more layers of conductive circuitry supported and separated by a dielectric material. Thus, printed circuit boards have outer layers and inner layers. The outer layers of a PCB are usually used for component placement and test pins.
A motherboard, or back plane, is an example of a printed circuit board (PCB). Components such as modules, connectors, subassemblies, and other printed circuit boards are often mounted on a motherboard. Interconnections on the motherboard are made utilizing traces on the board. The inner layers of a PCB also have circuitry. Plated vias are used to connect circuitry on different layers of the PCB.
The flowchart of a typical PCB build process is demonstrated in FIG. 1. Once the build process is initiated as shown in operation 100, the first phase, operation 110, involves designing the PCB. The design operation 110 involves building prototypes and is usually done using computed aided design (CAD) tools. The prototypes are then tested and evaluated in the next phase, operation 120, until the PCB meets all the design specifications. Once testing is completed, production begins in operation 130. Production typically includes processing the inner layer, processing additional layers, compressing or laminating the different layers together, drilling via holes, processing the outer layers, and adding components either manually or by machines. Following production, the board is reflowed or baked in operation 140. Then connectors are added in operation 150 and the back of the board is wave soldered in operation 160. Wave soldering is a process where an assembled PCB is brought in contact with a continuously flowing and circulating mass of solder. Once the board is completed, an adhesive identification label is added in operation 170. Finally, the board is tested again for functionality in operation 180.
A PCB typically consists of layers of fiberglass sheet laminated with etched copper patterns. FIG. 2 shows an example of a four layer PCB stackup. The four layers consist of two signal layers (layers 210 and 270), one power layer 230, and one ground layer 250. The signal layers 210 and 270 are conductive layers. The power and ground layers 230 and 250 help define the voltages delivered to the components added to the PCB.
A core layer 240 is sandwiched between the power layer 230 and ground layer 250. Unlike the signal layers 210 and 270, the core layer 240 is generally an insulating layer of dielectric material with copper adhered to both sides. The copper is used to form conductive circuits. The core material can be rigid or flexible.
A prepreg layer 220 exists between the signal layer 210 and the power layer 230. Similarly a prepreg layer 260 exists between the ground layer 250 and the signal layer 270. The prepreg layers 220 and 260, also known as the pre-impregnated layers, consist of the core material impregnated with a synthetic resin partially cured to an intermediate stage. The prepreg layers 220 and 260 are used to bond two materials together. Like the core layer 240, the prepreg layers 220 and 260 are insulating layers.
As previously stated, components are added to the PCB during the production phase of the PCB build process. FIG. 3 shows an example of a PCB 300 with placed components. In order to track the PCB, a bar code 310 is placed on the PCB along with other components such as the central processing unit (CPU) 320, rear I/O 330, expansion slots 340, and memory slots 350.
The bar code 310 is an adhesive label that is recorded and manually placed on the PCB 300. The bar code 310 is then manually tracked using a bar code scanner. The bar code label 310, however, must be placed in a component free area to ensure clearance for other components to be placed on the PCB 300.
Moreover, the bar code label 310 is typically required to be placed a pre-specified minimum distance from timing critical signals and busses to prevent possible performance degradation. The bar code label 310 can alter the impedance of traces on the PCB 300. Thus, the bar code label 310 is typically placed in low speed areas of the board 300.